Fig. 6. Structural interaction between Topi and Comr proteins. (A) Mapping domains of Comr responsible for the interaction with full-length Topi. Solid bars represent protein fragments tested in the yeast two-hybrid system against Topi. The region responsible for the interaction lies in the 200-300 amno acid fragment (bracket). (B) Mapping domains of Topi responsible for the interaction with full-length Comr. Zn-finger motifs within Topi are indicated with boxes. Fragments containing either the first two, or the final five, Zn fingers can bind Comr (brackets). (C) Co-immunoprecipitation of Comr and Topi from tissue culture. Cells expressed HA-tagged Topi and FLAG-tagged Comr or Smad1. Binding was assessed by IP-ing with anti-FLAG, and blotting with anti-HA (first pair of lanes) or vice versa (second pair of lanes). Topi and Comr co-immunoprecipitate in both cases (top). Total protein expression was assessed by western blotting of the cell lysate (bottom).